1. Field of the Invention
The present invention relates to a copper-based sliding material having high seizure resistance, and relates to a copper-based sliding material suitable for a plain bearing material.
2. Description of Related Art
Conventionally, a copper-based sliding material used for a plain bearing for an internal combustion engine is generally manufactured by a continuous sintering method. The continuous sintering method is a manufacturing method of continuously spreading Cu alloy powder on strip steel, and continuously performing sintering and rolling. A copper-based sliding material for a plain bearing is required to be free of Pb to respond to recent environment regulations, and a copper-based sliding material using a sintered Cu alloy containing Bi as an alternate material of Pb has been proposed. In the continuous sintering method, Cu alloy powder is spread on strip steel, but as shown in FIG. 6A, there are many gaps in a Cu alloy powder layer. When a temperature is then increased in a primary sintering step, as shown in FIG. 6B, Bi melts at about 270° C. into a liquid phase, and flows out from Cu alloy powder into the gaps between particles. At this time, sintering between Cu alloy particles is still insufficient, and Cu alloys have not been sufficiently bonded to each other. Thus, Bi flowing out into the gaps spreads along powder surfaces, and as shown in FIG. 5, Bi phase particles in a Cu alloy layer form a network. When the Bi phase particles in the Cu alloy layer form the network, the number of Bi phase particles connected in a depth direction from a sliding surface of the Cu alloy layer is increased. Thus, Bi in the Cu alloy layer melts and flows out to the sliding surface under a sliding environment, so that the amount of Bi in the Cu alloy layer is significantly reduced to deteriorate seizure resistance. Thus, it has been proposed to make Bi phase particles in the Cu alloy layer fine, thereby preventing Bi in the Cu alloy layer from melting and flowing out to the sliding surface to increase seizure resistance. For example, see Japanese Patent No. 3421724 (paragraphs 0007 and 0008), JP-A-4-28836 (page 2, right lower column, and page 4, right lower column), and JP-A-5-263166 (paragraphs 0010 and 0013).